About this calculator
Estimate concrete for strip foundations and trench-fill footings. Enter the total length of all runs, then the width and depth.
How it’s calculated
Volume = total length × width × depth, plus waste. For a rectangular building, the total length is roughly the perimeter. Measure along the centreline of the footing so the corners aren’t counted twice.
Worked example
With these inputs:
- Total footing length
- 18 m
- Width
- 600 mm
- Depth
- 225 mm
- Supply as
- Pre-mixed bags
- Bag size
- 25 kg
- Waste allowance
- 10%
the result is:
- Concrete needed
- 2.67 m³
- Net volume
- 2.43 m³
- Plan area
- 10.8 m²
- Ready-mix order (to 0.25 m³)
- 2.75 m³
- 25 kg bag
- 233 bags
Tips from the trade
- Dug trenches are rarely neat. Allow 10–15% waste, or more in sandy soil where the sides slump.
- Trench-fill foundations are often poured right up to near ground level. Use the real trench depth, not the drawn minimum.
- Order ready-mix with a little spare. Running short on a footing pour leaves a cold joint.
Common questions
How do I measure a footing perimeter?
Add the centreline lengths of every wall run. For a simple rectangle, that is 2 × (length + width) minus 4 × the footing width.
Results are estimates for planning and pricing. Check quantities against your drawings, the manufacturer’s data and the Building Regulations before ordering.